Control of Shroud Leakage Loss by Reducing Circumferential Mixing

Abstract

Shroud leakage flow undergoes little change in the tangential velocity as it passes over the shroud. Mixing due to the difference in tangential velocity between the main stream flow and the leakage flow creates a significant proportion of the total loss associated with shroud leakage flow. The unturned leakage flow also causes negative incidence and intensifies the secondary flows in the downstream blade row. This paper describes the experimental results of a concept to turn the rotor shroud leakage flow in the direction of the main blade passage flow in order to reduce the aerodynamic mixing losses. A threestage air model turbine with low aspect ratio blading was used in this study. A series of different stationary turning vane geometries placed into the rotor shroud exit cavity downstream of each rotor blade row was tested. A significant improvement in flow angle and loss in the downstream stator blade rows was measured together with an increase in turbine brake efficiency of 0.4 %.

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows: Part I — Design Concept and Typical Performance of a Swirl Breaker

“…The number of these swirl breaking ribs is the same as that of the rotor blades, that is, one rib is arranged per each pitch of the rotor blades. This number is smaller than the 8 cavity vanes per pitch used by Rosic and Denton [4]. The proposed swirl breaker, which is composed of just a flat plate rib, has a simpler structure than the past research examples.…”

“…In this case, they confirmed that the installation of baffles could improve the turbine performance by aligning the leakage flow to the mainstream flow direction before it left the cavity. On the other hand, Rosic and Denton [4] installed a small curved stator vane (i.e. a constant thickness blade) in the rotor shroud outlet cavity, and tested its performance.…”

“…In the present study, reduction of the tangential velocity of the rotor shroud leakage flow was the main focus. A tangential velocity removal device (called a swirl breaker) with a simpler structure than the bladelets and vanes of Wallis et al [3] and Rosic and Denton [4] was proposed, and its performance was evaluated by using CFD analysis and air turbine tests. This study is presented in two papers.…”

Experimental and numerical tip leakage flow visualization in the LP turbine labyrinth seal

“…Perfecting the aeroengine compartments is one of the areas with a significant impact on turbomachinery performance. Research by Rosic & Denton [1] shows 2% of turbine efficiency drop due to internal leakages. The labyrinth seals are the most popular solution to eliminate or regulate the leakage in aero-engines.…”

Uncertainty Quantification of Leakages in a Multistage Simulation and Comparison With Experiments

“…Traupel [8], Denton and Johnson [9], Denton [10], Gier et al [11], Rosic and Denton [12], Rosic et al [13], all tried to quantify these losses. However, the loss-generating mechanisms are highly dependent on the particular shroud and stage geometry, therefore it is difficult to develop universal design rules and to correlate different geometrical and operational turbine parameters to generic shroud design.…”